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T8030.hs:9:3: error:
• Couldn't match expected type ‘Pr a’ with actual type ‘Pr a0’
NB: ‘Pr’ is a non-injective type family
The type variable ‘a0’ is ambiguous
• In the ambiguity check for ‘op1’
To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
When checking the class method:
op1 :: forall k (a :: k). C a => Pr a
In the class declaration for ‘C’
T8030.hs:10:3: error:
• Couldn't match type ‘Pr a0’ with ‘Pr a’
Expected type: Pr a -> Pr a -> Pr a
Actual type: Pr a0 -> Pr a0 -> Pr a0
NB: ‘Pr’ is a non-injective type family
The type variable ‘a0’ is ambiguous
• In the ambiguity check for ‘op2’
To defer the ambiguity check to use sites, enable AllowAmbiguousTypes
When checking the class method:
op2 :: forall k (a :: k). C a => Pr a -> Pr a -> Pr a
In the class declaration for ‘C’
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